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Fire study will help project future carbon dynamics

Landscape: an area burned by the 2015 Boulder Creek Fire, one year later.
A severely burned area of the 2015 Boulder Creek Fire, British Columbia, one year later. High-severity fires historically were rare in this forest type. Photo courtesy Kate Peterson, University of British Columbia.

OREGON—In recent years, with summer temperatures on the rise, western Canada has faced several uncharacteristically intense fire seasons. In 2015, the Boulder Creek Fire caught the interest of scientists because of its notable size and severity.

Vicente Monleon, a research statistician at the Pacific Northwest Research Station, worked with colleagues from the University of British Columbia to take the opportunity presented by the atypical Boulder Creek Fire and explore its effect on postfire fuel and carbon dynamics.

“This fire was an unusual event in that it burned in the temperate coastal forests where large fires are very rare,” explained Monleon. “It is important to try to learn from this fire because these types of disturbances are predicted to become more common in the future in these coastal forests.” Fire behavior, severity, size and frequency are expected to shift with rising temperatures. The best way to crack the code of climate change and its effect on fire dynamics is to study these “new normal” fires as they occur.

Information on the effects of large wildfires in these forest types is lacking because there have been so few opportunities to study them. The Boulder Creek Fire was only the third wildfire in the region to burn more than 10,000 acres of coastal forest between 1950 and 2015. However, these moist temperate forests are important to the global carbon balance because of their high productivity, which enables them to sequester and store large amounts of carbon.

Monleon and his colleagues examined what happened to surface fuels after this severe wildfire, and what that means for carbon storage. Forest wildfires consume surface fuels, including fine materials such as grasses, twigs, and pine needles on the forest floor, all the way up to coarse woody material and whole trees. Combined, these fuels can account for almost one-quarter of total ecosystem carbon in some Pacific Northwest forests.

The Boulder Creek Fire burned mostly at moderate and high severity, leaving very few living trees. This will likely have long-term impacts on the forest carbon trajectories of the region. The scientists found that after the fire, carbon in the duff layer (the decomposing mat of vegetation that lies just above the soil surface) was significantly lower in plots burned at low severity compared with unburned plots.

“Overall, it was interesting to find that when you have a big fire, sometimes the total stored carbon does not change that much,” said Monleon. “We found that a lot of the fine fuels did burn, but a lot of carbon also stays in the system. There are now dead trees on the landscape, a lot of coarse woody material. It was more like a shift between carbon pools.”

This study also provides valuable baseline data on postfire surface fuels within the burn area of the Boulder Creek Fire. The scientists established permanent plots, which can be used as a starting point for longitudinal studies of postfire fuel and carbon dynamics in these coastal forests, providing unique information on the impacts of forest fires on surface fuels and informing the development of postfire management plans in a changing climate.

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